The present invention relates to a method and arrangement for determining position of a body provided with at least one marker object with a known dimension parameter, by means of at least one camera unit, provided with a sensor device and an optical element in a determinable distance from said sensor device, and means for retrieving and calculation.
Motion analysis is now a well-known method using camera unit and computer aid to analyse, e.g. biomechanichs of human, animals or motions of a robot arm etc.
In a simple system markers are attached to the object to be analysed. In the past the object provided with the markers was first filmed and then manually analysed and digitalised to determine the correct position of the markers. This was a time-consuming procedure.
Presently, cameras equipped with so-called CCD plates are used. CCD plate, which is a light sensor, is generally arranged in communication with necessary optical elements. A CCD plate, consisting of lines of charged coupled sensors arranged as a matrix, i.e. arranged in an X and Y coordinate system, for one or several colours, converts the light (from the optical element) projected on it, by electronically scanning in Y direction each line of X sensors and producing a television (video) signal. Then, the signals may be analysed in different ways to detect the position of the markers attached to the object.
Presently, two or more camera units are used to measure the distance to an object.
It is an object of the present invention to present a method and device to accurately determine the position, preferably the three dimensional position of an object using at least one camera unit, substantially in real time.
These objects are achieved by using a method, comprising steps of:
computing the coordinates of an image of said object reproduced on said sensor device,
computing a dimension parameter of said object corresponding to said provided dimension parameter,
calculating the proportion of parameters obtained to determine the position of said object.
The invention also concerns an arrangement for determining the position of a body provided with an object having a known dimension parameter to said body, said system comprising at least one camera unit, including a sensor device and an optical element, in a determinable distance from said sensor device, and means for retrieving and calculation, which is arranged to compute the coordinates of an image of said object reproduced on said sensor device, compute a dimension parameter of said object corresponding to said provided dimension parameter, calculate the proportion of parameters obtained to determine the position of said object and means for presenting the determined position.
Other advantageous embodiment according to the present invention are characterised in depending claims.